Navigation system



Sept. 23, 1952 A. M. MaCCALLUM EIAL NAVIGATION SYSTEM Filed Jan. 5. 1949 2 Sl-IEETS-SI-IEET 1 FIG. 1

HALVER INVENTORS 1- ALAN M MAC CALLUM SAB/NE L, BAR/NGfGOULO Y ATTORNEY I A. M. M CALLUM ETAL Sgpt. 23, 1952 NAVIGATION SYSTEM 2 SHEETS-Sl-IEET 2 Filed Jan. 5, 1949 INVENTORSY ozuscmmu o ALAN M MAC CALLUM SAB/NE L. BAR/NG-GOULD AT TOR NEY Patented Sept. 23, 1952 NAVIGATION SYSTEM? Alan M. :MacGalluni, Maywood, N. J., and Sabine L. Baring-Gould, New York,.N. Y., assignors to EBendix. Aviation Corporation, Teterboro, N. J a

. corporation of-Delaware 7 Application January 5, 1949,=S,efla;l?No.-G9,"388

This invention generally relates to navigation systems-for mobile craft such as aircraft, for

example, and more particularly constitutes an improvement over the directionindicating and/or maintaining means described and claimed in toopending application Serial No. 61,343, filed November 22, 1948, and assigned to the assignee of thepresent'appl-ication. v

Wl'iere the arrangementfiof the above men tioned copending application-requirestwo torque amplifier systems 'for correcting a directional gyroscope for errors due to wandering of the gyro withoutprecessing the gyro thearran'gemerit of the present invention requires but a single "tor ue amplifier system for accomplishing substantially the same result in-a simpler mannergthereby materially reducing the wei ht as well as the 'costof the entire arrangement.

An object of the present invention, therefore, isitomrovide a novelc'omoass or reference system utilizing a free directional gyroscope for use with mobile craft.

Another object of the invention is to provide a novel navigation system for mobile craft utilizinga directional gyroscope in "which the azimuth information provided byfthegyro is 001'- rected'by a reference provided byth'e earths magnetic field .or any other suitable reference in azimuth. 7 I

A -further object is to provide a novel-compass system for mobile craft comprisingboth a magnetic "compass and a directional gyroscope combined in anovel and simple manner.

Another object is to provide a novel directio indicating and/ or maintaining mean utilizing a directional gyroscope "in which the conventional requirement for corrective precession 'onrthe gyro has been eliminated, 'therebyehminating the need for .precessing expedients whichhave been heretofore required on the gyro rotor.

.A still ifurther object is .to provide ;a ":novel compass :system comprising :a magnetic compass and adirectional gyroscope 'tcgether withasing'le torque amplifier which is "energized alternately by thecompass and the gyro to operate adesired controlled member :suoh'as an indicator, an automatic pilot system or for stabilizing in azimuth of any other desireddevice crapparatus.

The above and fu'rther objects and novel features of the invention will more fully appear from the following detailed ,description -when the in "the drawings, wherein like "reference chan,

'acters refer to like parts in both views;

Figure "1 is a diagrammatic illustration of the I .15 teams. (01. ea-222) novel navigation system. f'the present-invention; and

:Figure 2 i'sa view, similar to Figure 1, .ofa modified form Of the invention.

Referringnow to the drawings for-a more detailed description of the present invention and more particularly to Figurel thereof, a conventional .three-degree-of-freedom directional gyroscope I0 is shown having a rotor H, provided with a horizontal spin axis, which is mounted by-wayof minorhorizontal trunnions 12 within a gimbal l3,'the latter being provided with vertical .trunnions -I4 mounting the gyro within 5a 1 suitable casing (not shown). Inasmuch-as a gyro ofithis character will maintain a fixed reference iii-space, it is connected, in :amanner to-presently appear, to indicating means such as a pointer 15 which is movably mounted relative to a dial it having a-compass scale thereon, the dial "being fixed to the craft. 1

As is well known, pointer I5 isstabilized in azimuth by the directonalgyro so that any departure by the craft'from a prescribed coursewill be manifested by relative motion-of the dial and pointer. Due to hearing friction and other causes,however, the gyro is subject to wandering which, if uncorrected, would lead to erroneous courseindication. A novelmonitoring system is provided, therefore, in the form of .an earth inductor device 1! which, in accordance with'the present invention, will periodically'correct pointer position and thereby'correct for gyro wandering =if suchha's occurred without precessing the gyro, i. .e., the gyro is free of conventional precessing expedients and permitted to wander at will but pointer displacement due to gyro wandering is corrected.

"Pointer i5 is primarily under "the control of gyro ll! and for this purpose one of trunnions [4 of the latter supports, for movement therewith, a wound "rotor 18 of a variable inductive devicehaving a wound stator l9, thelatter being movably-supnortedby a suitably journalled shaft 20. Stator i9 is connected by way of leads '2! to a second wound stator 22, which 'is fixed with respectto the craft, of "a coordinating inductive device having a wound rotor 23 mounted on a movable shaft'24 which also mounts pointer I 5 thereon. V v

Rotor winding 3 is grounde'd a't one end as shown and at its other end is connectedby'way of a lead 25, a fixed contactZG and a movable contact 21 with asuitable source "of alternating current (not shown). 'With rotor l8 energized, signals will appear in stator windings I 9 which will be communicated to stator windings 22. If

of the energizing current depending upon the phase of the signal induced within rotor 23, of

\ a suitable Shaft 31 supports a pair of spaced bevel gears j 38 and 39 thereon, the former being adaptedfor. driving engagement with, a bevel gear 40 carried on shaftZfl and the latter for engagement with a bevel gear 4| carried by shaft 24. Shaft 31 also mounts a core 42 of a solenoid 4 thereon, the solenoid,'when energized, drawing shaft 31 to the right against the action of a spring 44 which normally urges the shaft to the left. Solenoid 43 is arranged to be energized at the time that rotor winding I8 is energized and has one side thereof grounded, the other side thereof connecting with a battery 45 by way of a lead 46, a movable contact 41 anda fixed contact 48. Energization of the solenoid causes gear 38 to disengage gear 40 and gear 39 to engage gear 4| sothat motor 32 will drive rotor 23 to a null relative to its stator 22 at which time the signal of the rotor drops to zero to de-energize the motor. In this manner pointer I5 is positioned relative to dial l6 by the directional gyro. Since it will now be apparent that pointer I5 is sub ect to any gyro wandering, the monitoring system including the earth inductor device I1 is provided. in accordance with the present invention, for correcting pointer movement due to such wandering. Device I! generally consists of three laminations 49, and 5| arranged in triangular relation, each lamination supporting a secondary winding 52, 53 and 54 thereon, like ends of each winding being connected at a common midpoint and the opposite ends of each winding connecting by way of leads 55 with stator 22 of the coordinating inductive device. An energizing winding 56 is carried by the laminations, one end of the latter winding being grounded and the opposite end thereof connecting by way of a lead 51, a movable contact 58 and a fixed contact 59 with a conventional frequency halver 60, the purpose of which will presently appear. e As is well known with the use of such device inductive device I1 may be pendulously mounted or gyro stabilized in the earth's magnetic field and, as a result of relative displacement of the device and the field, signals will appear at the secondaries proportional to the angular displacement of the laminations with respect to the field. The signals at the output of the secondaries are at a frequency double the frequency of the current in theenergizing winding and in order that the frequencies at stator windings l9 and the secondary windings of device l1 will be the same, so that the frequencies of the current supplied to variable phase 3| of motor 32 will be the same, the frequency halver 60 is utilized between energizing winding 56 and the source of current for energizing rotor winding I8. If, for example, a 400 cycle supply is associated with movable contact 21, a 200 cycle'supply will be available at fixed'contact 59;

Assuming now a condition in which movable contact 58 is in engagement with fixed contact 59 and movable contact 41 is out of engagement with fixed contact 48, solenoid will be deenerg'ized so that spring" wm ur'ge bevel gear 38 into'engagement with bevel gear 49 and disengage bevel gear 39 from gear 4|, and the output of frequency halver 60 will energize pri- 'mary winding 56 of inductive device I1. pending upon the angular disposition of device in the earths magnetic field, signals will be developed at'secondaries 52, 53 and 54 which are communicated to stator windings 22 by way of leads 55. Where the positions of both the directional gyro and'inductive device I! are the same (both positioned due north, for example), rotor winding 23 will be normal to the resulant flux vector at stator 22 resulting from energization of either rotor winding 18 or primary'winding 53 of device I! so that the entire system is syn-, chronized. I

If, on the other hand, rotor 23, previously positioned by gyro I0, is at some position other than normal relative to the resultant flux vector at stator 22 due to energization of primary winding 56, a signal will be induced therein and amplified within amplifier 30 to energize motor 30 which, under this condition, will displace stator |9 relative to its rotor [8, the latter being deenergized at this time. The presenceof a signal in rotor 23 indicates that the system is-out of synchronism and the object of displacing stator l9 relative to its rotor I8 is to so position the latter stator that upon energization vof rotor I8 the flux vector at stator 22 due to energization of rotor |8 or primary winding 56 will be the same thereby re-establishing the synchronized condition of the system. Positioning of stator I9 in this manner toa null position is not necessarily accomplished automatically during a single period of control by the earth inductor but the initial movement of the stator is such as to reduce the error signal, the time required for positioning. the stator in the null position being determined by the amount of the error signal as well as the selection of the period of control by the earth inductor. If displacement of stator |9 by motor 32 has been other than that necessary tore-establish the synchronized condition of the system, a signal 'will 'again appear at rotor 23, after primary winding 56' has been de-energized and solenoid 43 and rotor 8 have been energized with gears 38 and 40 disengaged and gears 39 and 4| re-engaged' Such signal again energizes motor 32 to drive'rotor 23 in the direction which is initially towards a null. Thereafter, rotor|8 is again de-ener'gized and primary winding 56 is energized while solenoid 43 is de-energized, the foregoing steps being repeated until, with either rotor '|8 or winding 56 energized, no signal will appear at rotor 23.

During normal operation of the system for direction indication and/or maintenance it is desirable to maintain rotor winding l8 and solenoid 43 energized for a period of time longer than the time that winding 56 is energized and soleold 43 de-energized. As a result, during normal operation, pointer I5 is under primary control by the gyro, the monitoring control being provided for only short periods of time. On the other hand, where there is initially a wide divergence between the gyro and device H and it is desired to synchronize the system prior to normal operation thereof, it is desirable to maintain winding .56 energized for a period of time longer than that .during which rotor l8 is energized. I

The means for alternately pulsing or energizing aen rae 5f rotoirwlndingt is. of l'llonprimarywinding 56. oi inductivedevice Ll take.- anyiormanda as shown in Figure. 1 may comprise: at. bimetallic;

element 6| having a heating coil 62 woundthere- 6 5- and. 10, the. former for cooperation with. La-

fixed contact H and the latter for. cooperation. with afixed contact. 12 r A reversing mechanism, whereby primary winding. 56 of device I! may, be initially ener-- gi'zedfor synchronization PLUIPOSQSiiOI aperiod of time longer thanthat underwhich rotor H3 is. energizedis provided inthe form at a second; bimetallic: element 13 having a heating coil. M- wound thereon. one. end of. the. coil being con.-

nected with one. side of. a battery'ii and. the

other end of the coil being: adaptediorconnecti'on with the opposite side of; the. battery by way of a switchfl-fil Themov-able. end of element E3 is provided. with an upper and lower contact H and 1-8, the. former cooperatingwith o a fixed contact l9; connectedwith. fixed contact; H and. the latter cooperating with. a. fixed.- contact 86. connected with fixed contact 12. Closely adjacent contacts H and. [8 on element 13 is a.

further contact: 81 which connects by way of a. lead 82 with; the opposite sideoirelay 6,6.

Assuming a wide; divergence. between the; di-- rectional gyro and inductive device H, synchro nizationleadingto normal operation of. the systern is obtained by closing switches I6 and 61a. whereupon current .flows in; both; heating coils 62 and 14. and relay 6.6 is simultaneously energized by battery is;

relay, an armature, 8.3. .is pulled. downwardly drawing movable contacts. 2], 4.1 and. 58' therewithwhich are connected thereto. by a, common member.84.. As a result, contacts 58, 51%. areengaged to: energize primary: winding .56.. of device I! and contact 41: is disengaged. from contact is to die-energize solenoid 43 whereby gears 38 and R to are engaged and: gears 39 and M1 are-disengaged. Under; this condition, stator Hz is. displaced by the signal output: oi device I? connected to. stator 22.

Bimetallic element lit and itsheating. coil 61' while. bimetallic element actszas a merino-pulsar ii-l. and. its. heating coil 14 acts. as a .clelay device, Initially;. with switches iii and 61a closedycontacts l1 and 190i the delay device and contacts 69- and ii of the pulser are engaged so thatprh mary winding 5b is energized. Atrthe same. time that contacts 59: ll oithe pulser' are closed, contacts 63 and. 64: thereof are. also; closed; so that coil. 62 heats up and aftera predetermined interval of time. element 61 bends about itsfixed end. to. disengagecontacts 69: and 64 from, their related contacts it and .63 as. a result of which. relay 66 becomes de-energized so that its moo able contacts 21,. 4:1 andftlfl engage. with fixed. contactsrzfig ia and an open contaettfi: In this manner primary-winding 7 both solenoid. 43. and. rotor l8v are energizedso that the: gyro drives rotor23to. anull it: has not yet attained that position. At the same time; coil .62 cools; oft to" permit element. M to assume its. original position to again. close.- contacts 69,.

Upon. energization. oi the,

developedin rotor 2&3. by; the

56 is de-energizedand.

. 6:. Itand. 63,, 84 to. energize rclayxfifi. andtthus.

connectgthe gyroirom the; systemand place.the.:, latterunder the control of: device. [1. .Inasmuch.

as contacts 1.1,. '19.: of the. delay device: arein ens" gagement. at. this time. pointer; 15.. is under: cons trol of; inductive. device L] for a longer period of: time than it is. under the. control of. the gyro- This results fromthefactthatit takes element 6.Il a longer period of time to heat up. than'it does forait: to cool. ofii.

After: a. 'predeterminedinterval of time has:

lapsed, coil M will have heated bimetal; element; I3: sufficiently to cause the. latter to .bendabout its fixed .end to. disengage contacts. ill,..i91.and'en- (gage. contacts; 78; 80.. Once element 13' has. bent."

downwardly it remains in. such: position for-"so long as the. system operates. Withcontacts. T8;

86 engaged, the-pulsing cycle reversedsothat rotor. l8 of the gyro. as well. as solenoid 43.. are

energized for a. period of time longer than that under. which winding 56 is energized and the solenoid de-energized. This occurs because. when; element. 6 I is in the positionshown contacts 63:; 64 are engaged and place. coilBZ across battery:- 68. whereupon the. element heats. up andbends downwardly to disengage contacts 63, 6:1 to deenergize the coil and engage. contacts 70,12 to energize relay 66 at which time control by device- I1 is inserted intothe system and control by the.

its; cooling off, element 6|. bends upwardly to're-. engage contacts. 63, 6.4 and .de-energizethe relay to insert gyro control into the system and disconnect control by device, H. The. period during which relay 66 is energized is shorter thanthe;

period during whichit is (lo-energized so that gyro. control of. the. system occurs a maiorporuv tion of thetime. 4

In the foregoing manner the entire systemiis. synchronized. through coordinating device 22- 23, which alternately compares the position of.

the gyro and inductive device ll. Thereafter, when any wanderingof; the gyro occurs the. signals induced within stator 1.9., due torelative movement of rotor 18, will be communicated to stator 22 where the resultant flux vector will be displaced relative to rotor 23to thereby'disturb the synchronized relation of the system. At such; time, due to the signal inducedtherein, rotor 23: willbe driven. to. a new null relative to its stator and .during the next cycle, when device 11 is en.-

ergized and rotor 18 de-energized; stator 19 will be displaced. relative to its rotorso. that during the; following cycle, when'rotor {8' is-agai'n reenergized and device ll de-energized, the IfillX vector at stator 22. will again be displaced relative to rotor 23 in an opposite direction. to induce a signal in'the latter whereupon, rotor 23 will be driven to its original. null position. In this .man-

ner even though the. gyro wanders, the pointer I or any other member controlled, by shafted,v due to monitoring action of device I? maintains a fixed reference position in azimuth.

With the form of the inventionof Figure 1,.

above described, the dial and pointer. arrangement is. adapted for location within thecasinglof. directional gyro IQ. It. may, howeverybe desire. able to have the indicating means. or other. con-. trolled member located remotelyirom the direc: tional gyro andto this end the system. oiFigure 2 is provided in which parts having counterparts;

inFig-ure 1 are designated with the same reference-charactersplus 100. In this-latter formof the invention,.-stator H9 is. fixed relative to move able rotor H 8. supported by trunnion I I4: of gyro:

;l in; and stator I22 of the co.ordinating :.devicei is gyro: is removed. from. thesystemt Because of:

placement relative to its rotor I23. Inasmuch as stator I22 is displaceable in this form of the invention, one end of shaft I86 is provided with a pinion I81 which drives dial II6 therewith through a gear I88. In this manner a desired fixed relation of the dial relative to the stator of the coordinating device is maintained. The opposite end of shaft I86 carries the bevel gear I40 which under certain conditions is adapted for drivable engagement with bevel gears I38 carried by shaft I31.

Except for the changes noted above, the system of Figure 2 is the same as that of Figure 1 and operates in substantially the same manner. Relay I66 is connected by way of leads I65 and I82 to the thermo-pulser and the delay device of Figure 1. Upon closure of switches 61a and 78 the entire system, as before, is initially under longer control by device II'I than it is by gyro IIO. Once the delay device operates to disengage contacts I1, I9 the cycle is reversed so that primary control of the system is effected by the gyro with monitoring action by device I I1.

When the cycle is of such nature that both rotor I I8 and solenoid I43 are energized and some discrepancy in the position of the directional gyro and device III has occurred, a signal will be induced within rotor I23 which is amplified within amplifier I30 to actuate motor I32. The motor thereupon drives rotor I23 to a null and displaces pointer I I5 therewith. Pointer position thus is made to correspond with gyro position. As the next cycle occurs, rotor II8 becomes de-energized as does solenoid I43 and winding I56 of device II'I becomes energized. Inasmuch as the pointer has been moved from its fixed reference position in azimuth, the flux vector at stator I22 will be displaced to some position other than normal rel ative to rotor I23 so that a signal is induced in the latter to energize motor I32 which, under this condition, because gears I38 and I40 are now engaged, will displace both stator I22 and dial IIB, motion of the stator and the dial continuing until the flux vector at stator I22 is brought to a normal relation with respect to rotor I23. For each displacement of the pointer relative to the dial due to wandering of the gyro the system is so monitored by device III that the dial, in turn, is displaced relative to the pointer. Thus the pointer relative to the dial maintains a fixed reference position in azimuth as desired even though the gyro is permitted to wander at will.

While the coordinating device of both forms of the invention is shown as operating indicating means it can equally as well control an automatic pilot system, for example, by providing a reference signal therefor in which case a further in-v ductive device would be provided so that its rotor would be displaceable by shaft 24 of Figure 1. In the form of the invention of Figure 2, such inductive device would have its rotor movable by the shaft supporting rotor I23 and its stator movable by shaft I86.

While the reference providing means for the monitoring system is shown as comprising a pendulously mounted or gyro stabilized earth inductor device I! it could equally as well be a damped magnetic compass with an inductor device disposed in the magnetic field of the needle of the compass.

Although but two embodiments of the invention have been illustrated and described in detail it is to be expressly understood that the invention is not limited thereto. Various changes may be. made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

We claim:

1. Means comprising a controlled device for maintaining a fixed reference position in azimuth, coordinating means for operating said controlled device, means comprising a directional gyro for energizing said coordinating means, reference means comprising an earth inductor device for energizing said coordinating means for correcting said controlled device for wandering of said gyro, and periodically operable means for alternately connecting said directional gyro to said coordinating means and energizing said reference means.

2. Means comprising a controlled device for maintaining a fixed reference position in azimuth, coordinating means comprising a two-part inductive device for operating said controlled device, a directional gyro, an electrical pick-oil operable by said gyro, said pick-01f when energized controlling said coordinating means, reference means which when energized controls said coordinating means for correcting said controlled device for wandering of said gyro, and means for alternately energizing said pick-oil means and said last-named reference means.

3. A navigation system comprising controlled means for maintaining a fixed reference position in azimuth, a directional gyro, means comprising an electrical pick-off operable by said gyro, said pick-off when energized operating said controlled means, reference means which when energized operates said controlled means to correct the latter for errors due to wandering of the gyro, and means for alternately energizing said pick-oiI means and said last-named reference means.

4. Direction indicating means comprising relatively movable pointer and dial elements, a coordinating device connected for operating at least one of said elements, means comprising a directional gyro for controlling said coordinating device, reference means comprising an earth inductor device for controlling said coordinating device to correct for errors due to wandering of the gyro, and periodically operable means for subjecting said coordinating device to alternate control by said reference means and said directional gyro.

5. Direction indicating means comprising a relativelymovable pointer and dial. a coordinating device connected for moving said pointer,-

means comprising a directional gyro for controlling said coordinating device, reference means comprising an earth inductor device for controlling said coordinating device to correct for errors due to wandering of the gyro, and intermittently operable means for subjecting said coordinating device to alternate control by said directional ordinating device to alternate control by said directional gyro and said reference means.

7. In combination with controlled means for maintaining a fixed reference position in azimuth, means comprising a directional gyro, reference means comprising an earth inductor device, and

9 cyclically operable means subjecting said controlled means to alternate control by said directional gyro and said reference means.

8. In combination with a controlled member for maintaining a fixed reference position in azimuth, coordinating means for operating said controlled member, means comprising a directional gyro, reference means comprising an earth inductor device, and cyclically operable means subjecting said coordinating means to alternate control by said directional gyro and said reference means.

9. Direction indicating means comprising relatively movable pointer and dial elements, a coordinating device connected for operating at least one of said elements, a directional gyro, means comprising an electrical pick-off operable by said gyro, said pick-off when energized operating said coordinating device, reference means which when energized operate said coordi ergized operating said coordinating means to correct for errors due to wandering of the gyro, and means for alternately energizing said pickoff device and said reference means.

11. A navigation system for a mobile craft comprising controlled means for maintaining a fixed reference position in azimuth, coordinating means for operating said controlled means, a directional gyro adapted for connection to and disconnection from said coordinating means, said directional gyro when connected to said coordinating means influencing the latter whereby said controlled means is operated during craft deviation from a prescribed course, reference means comprising a stationary earth inductor device fixed on said craft and connected to said coordinating means and adapted for energization and de-energization, said reference means when energized correcting said controlled means for wandering of said gyro, and means for alternately connecting said directional gyro with said coordinating means and energizing said reference means. 1

12. A navigation system for a mobile craft comprising controlled means for maintaining a fixed reference position in azimuth, coordinating means for operating said controlled means, a directional gyro adapted for connection to and disconnection from said coordinating means, said directional gyro when connected to said coordinating means influencing the latter whereby said controlled means is operated during craft deviation from a prescribed course, reference means comprising a stationary earth inductor fixed on said craft and connected to said coordinating means and adapted for energization and deenergization, said reference means when energized correcting said controlled means for wandering of said gyro, and means for alternately connecting said directional gyro to said coordinating means and for de-energizing the reference means during one interval of time and for disconnecting the directional gyro from said 00- ordinating means and for energizing said reference means during a second interval of time.

13. In combination with controlled means for maintaining a fixed reference position in azimuth, means comprising a directional gyro, reference means comprising an earth inductor device, cyclically operable means subjecting said controlled means to alternate control by said directional gyro and said reference means, and means operatively connected with said cyclically operable means and effective after a predetermined interval of time to modify operation of said cyclically operable means whereby said controlled means is under the control of said directional gyro for a longer period of time than it is under the control of said reference 14. In combination with controlled means for maintaining a fixed reference position in azimuth,

means comprising a directional gyro, referencev means comprising an earth inductor device, cyclically operable means subjecting said controlled means to alternate control by said directional gyro and said reference means, and means operatively connected with said cyclically operable means and effective during a predetermined interval of time to modify operation of said cyclically operable means whereby said controlled means is under the control of said reference means for a longer period of time than it is under the control of said directional 15. In combination with controlled means for maintaining a fixed reference position in azimuth, means comprising a directional gyro, reference means comprising an earth inductor device, periodically operable means subjecting said controlled means to alternate control by said directional gyro and said reference means, and means connected with said periodically operable means and effective during a predetermined interval of time for controlling the operation of said periodically operable means whereby said controlled means is under the primary control of said reference means and effective following the predetermined interval of time for modifying the operation of said periodically operable means whereby said controlled means is under the primary control of said directional gyro.

ALAN M. MACCALLUM. SABINE L. BARING-G OULD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,014,024 Leatherman Sept. 10, 1935 2,076,328 Wade et a1. Apr. 6, 1937 2,108,263 LAbee-Lund Feb. 15, 1938 2,357,319 Esval et a1. Sept. 5, 1944 2,414,128 Sinks Jan. 14, 1947 FOREIGN PATENTS Number Country Date 49,251 France Nov. 12, 1938 (Addition to No. 793,301) 

